Synthesis, characterisation, crystal structures and reactivity of a series of ruthenium-cobalt mixed-metal nitrido carbonyl clusters with iodide ligands

Reaction of [Ru3(μ-H)2(CO)9(μ3-NOMe)] (1) with two equivalents of [Cp*Co(CO)I2] (Cp*=η5-C5Me5) in refluxing THF resulted in the isolation of four new heterometallic tetranuclear nitrido clusters, namely [Ru3CoH(μ-H)(CO)6(Cp*){μ-η2-C(OMe)O}(μ4-N)(μ-I)2] (2), [Ru3Co(μ-H)2(CO)6(Cp*){μ-η2-C(OMe)O}(μ4-N)I(μ-I)] (3), [Ru3Co(μ-H)2(CO)6(Cp*){μ-η2-C(OMe)O}(μ4-N)I(μ-I)] (4) and [Ru3Co(μ-H)2(CO)8(η5-C5Me5)(μ4-N)(μ-I)] (5), together with a triruthenium nitrene cluster [Ru3(μ-H)3(CO)8(μ3-NOMe)I] (6) in moderate yields. The first four clusters have either a chain (2) or a spiked triangle (3-5) metal skeleton with the central nitrido atom capping all four metal atoms; alternatively, these four clusters can also be viewed as having a highly distorted butterfly arrangement. Clusters 2, 3 and 4 are isomers with different ligand dispositions. The hinge and an Ru-Ru wing-edge are missing in 2, whereas a wing-edge is lost in each of 3 and 4 (Ru-Ru) and 5 (Ru-Co). Opening up the hinge metal-metal bond has a significant effect upon the nitrido chemical shift in the15N-NMR spectrum. Clusters 3 and 4 differ from each other in the coordination site of a terminal iodide ligand, and both clusters are inter-convertible under vigorous conditions. Cluster 6 is a trihydrido nitrene cluster with a terminal iodide ligand.15N-NMR studies were performed in order to investigate the environment of the nitrogen atoms in these nitrido and nitrene clusters.